1. Field of the Invention
The present invention relates to a speed change gear for an automatic transmission for achieving at least six forward gears and one reverse gear, which speed change gear is constituted of an input portion, three planetary gear sets, three clutches, two brakes and an output portion. Hereinabove, the at least six forward gears and one reverse gear are achieved by properly engaging and disengaging the three clutches and the two brakes.
2. Description of the Related Art
U.S. Pat. No. 5,106,352 {equivalent of Japanese Patent Unexamined Publication No. Heisei 4 (1992)-219553} discloses a conventional speed change gear for an automatic transmission, which speed change gear is constituted of an input shaft, one single pinion planetary gear set, a Simpson planetary gear train (combination of two single pinion planetary gear sets), three clutches, two brakes, and an output shaft. The conventional speed change gear for an automatic transmission according to U.S. Pat. No. 5,106,352 {equivalent of Japanese Patent Unexamined Publication No. Heisei 4 (1992)-219553} achieves six forward gears and one reverse gear by properly engaging and disengaging gear change elements, namely, the three clutches and the two brakes.
The speed change gear for the automatic transmission having the one single pinion planetary gear set and the Simpson planetary gear train as described above has the following feature (1) and feature (2):
(1) The first gear of the Simpson planetary gear train may cause a maximum torque. A torque flow at the first gear may be born via all members, which is advantageous in terms of strength.
(2) Compared with a sun gear input, the Simpson planetary gear train bringing about a ring gear input may cause about half tangent force, which is advantageous in terms of gear strength, gear life, carrier rigidity and the like.
Contrary to the above feature (1) and feature (2), the one single pinion planetary gear set and the Simpson planetary gear train according to U.S. Pat. No. 5,106,352 {equivalent of Japanese Patent Unexamined Publication No. Heisei 4 (1992)-219553} may also have the following problem (3) and problem (4):
(3) Obtaining an over drive O/D gear shift is supposed to make a carrier input to the Simpson planetary gear train. Making the input shaft and the output shaft substantially coaxial with each other, however, cannot form a carrier input path in the single pinion planetary gear set since the single pinion planetary gear set is constituted of limited three rotation members.
(4) Forming the carrier input path, therefore, needs to dispose the input shaft and the output shaft substantially in parallel on different axes, thus making the automatic transmission radially enlarged.
For solving the above problem (3) and problem (4), U.S. Pat. No. 5,106,352 {equivalent of Japanese Patent Unexamined Publication No. Heisei 4 (1992)-219553} further proposes a speed change gear using a Ravigneaux compound planetary gear train (double pinions each meshing with a sun gear) replacing the Simpson planetary gear train, as is seen in its FIG. 13, FIG. 14 and FIG. 15.
The speed change gear with the Ravigneaux compound planetary gear train may, however, cause the following problem (5), problem (6), problem (7) and problem (8), although all elements are disposed substantially coaxially (in other words, with parallel disposition of elements avoided):
(5) A double pinion planetary gear set on one side of the Ravigneaux compound planetary gear train may bear a maximum torque (at first gear) of the gear train, which is disadvantageous in terms of strength.
(6) A torque increased with the one single pinion planetary gear set (as a speed reduction gear) is to be inputted to the sun gear of the Ravigneaux compound planetary gear train may cause a greater tangent force than the ring gear input, which is disadvantageous in terms of the gear strength, the gear life, the carrier rigidity and the like.
(7) At the first gear, securing strength (gear strength and gear life) of the Ravigneaux compound planetary gear train and improving the carrier rigidity and the like need to enlarge the Ravigneaux compound planetary gear train, thus making the automatic transmission enlarged. In sum, the Ravigneaux compound planetary gear train""s coaxial disposition of the elements (input shaft and output shaft) contributing to small speed change gear may be set off.
(8) Some gear shift(s) may cause a torque circulation to the Ravigneaux compound planetary gear train, thus lowering transmission efficiency leading to increase in fuel consumption.
In other words, the speed change gear having the one single pinion planetary gear set and the Ravigneaux compound planetary gear train may cancel the feature (1) and the feature (2) of the speed change gear having the one single pinion planetary gear set and the Simpson planetary gear train. In addition, the speed change gear having the one single pinion planetary gear set and the Ravigneaux compound planetary gear train having the problem (3) and the problem (4) may enlarge the automatic transmission.
En passant, U.S. Pat. No. 5,106,352 {equivalent of Japanese Patent Unexamined Publication No. Heisei 4 (1992)-219553} also discloses in FIG. 12 the single pinion planetary gear set reducing rotation of the great torque, which rotation is inputted to the ring gear of the Ravigneaux compound planetary gear train. In this case, however, the input portion and the output portion are disposed substantially in parallel, instead of substantially coaxially, thus enlarging the automatic transmission.
It is an object of the present invention to provide a speed change gear for an automatic transmission.
It is another object of the present invention to provide an input portion and an output portion disposed substantially coaxially without using the Ravigneaux compound planetary gear train, with the feature (1) and the feature (2) obtained by the Simpson planetary gear train kept {more specifically, with the advantages (gear strength, gear life and the like) of the gear train kept}, with the problem (3) and the problem (4) (making the automatic transmission enlarged) solved, and with the problem (8) (torque circulation caused to the Ravigneaux compound planetary gear train, and increased fuel consumption) solved.
It is still another object of the present invention to provide the speed change gear for the automatic transmission with improved selectivity of gear ratios, as compared with the speed change gear using the Ravigneaux compound planetary gear train.
It is still another object of the present invention to provide the speed change gear for the automatic transmission which speed change gear can shorten a power conductive paths (including clutches) transmitting a great torque reduced in a first planetary gear set to a latter planetary gear set(s), can make component parts for the power transmission smaller and facilitate handling and mounting of the component parts, can keep the above feature (1) and feature (2), and can contribute to making the automatic transmission smaller.
According to an aspect of the present invention, there is provided a speed change gear for an automatic transmission, comprising:
1) an input portion for inputting a rotation from a power source;
2) an output portion disposed substantially coaxially with the input portion;
3) three planetary gear sets including a first planetary gear set, a second planetary gear set and a third planetary gear set for providing a plurality of power conductive paths to an area defined between the input portion and the output portion; and
4) a first clutch, a second clutch, a third clutch, a first brake and a second brake to be selectively connected and disconnected in such a manner that the three planetary gear sets change a rotation from the input portion at a corresponding gear change ratio by selecting one of the plurality of the power conductive paths, thereby outputting the thus changed rotation to the output portion, the first clutch, the second clutch, the third clutch, the first brake and the second brake making a combination of engagement and disengagement, the combination making a selection from at least six forward gears and one reverse gear.
One of the three planetary gear sets is a speed reduction planetary gear set for continuously reducing the inputted rotation and outputting the thus reduced rotation.
One of the remaining two planetary gear sets of the three planetary gear sets is a double sun gear planetary gear set which includes;
two sun gears, a common pinion meshing with the two sun gears in common, one ring gear meshing with the common pinion, and a planetary carrier for carrying the common pinion in such a manner that the common pinion rotates, the planetary carrier being adapted to input and output a rotation from between the two sun gears via a center member connected to a side member.
The other of the remaining two planetary gear sets of the three planetary gear sets is a single pinion planetary gear set which includes;
one sun gear, a pinion meshing with the one sun gear, one ring gear meshing with the pinion, and a planetary carrier for carrying the pinion in such a manner that the pinion rotates.
The speed change gear for the automatic transmission includes:
i) a first rotation member including one of the two sun gears of the double sun gear planetary gear set, and being adapted to be held stationary by the second brake;
ii) a second rotation member including the other of the two sun gears of the double sun gear planetary gear set, and receiving via the second clutch the reduced rotation from the speed reduction planetary gear set;
iii) a third rotation member including an element connected mutually to the double sun gear planetary gear set and the single pinion planetary gear set, and outputting the changed rotation to the output portion;
iv) a fourth rotation member receiving via the third clutch the inputted rotation, being adapted to be held stationary by the first brake and including an element in the double sun gear planetary gear set and the single pinion planetary gear set; and
v) a fifth rotation member receiving via the first clutch the outputted rotation from the speed reduction planetary gear set, and including an element in the corresponding one of the double sun gear planetary gear set and the single pinion planetary gear set.
One of the double sun gear planetary gear set and the single pinion planetary gear set which relates to the second rotation member and the fifth rotation member is disposed nearer to the speed reduction planetary gear set than the other of the double sun gear planetary gear set and the single pinion planetary gear set.
The other object(s) and feature(s) of the present invention will become understood from the following description with reference to the accompanying drawings.